Every citizen of India whose name is not included in the electoral roll, and who has not acquired the citizenship of any other country and who is absenting from his place of ordinary residence in India owing to his employment, education or otherwise outside India (whether temporarily or not) is entitled to have his name registered in the electoral roll in the constituency in which his place of residence in India as mentioned in his passport is located following the insertion of a new section 20 (A) in the Representation of the People Act, 1950 by Representation of the People (Amendment) Act 2010. There is a facility of on line registration (http://www.nvsp.in/forms/form6a.html) for NRI electors available in NVSP portal of ECI. The link takes the applicant to the National Voters' Service Portal and by clicking 'Apply online for registration of new voter' a new window with Form 6 opens which can be filled up and submitted online.
Steps for submission of Form 6a at NVSP portal of ECI for overseas electors is attached herewith. Web link for FAQs - Overseas (NRI) electors is available at link : http://eci.nic.in/eci_main/nri/NRI_2122013.pdf